1. Field of the Invention
The subjects of the invention are a process for connecting an integrated circuit and the external terminals of a package, and the resulting integrated circuit package and data processing installation. It is more particularly suited to integrated circuits which run at very high speed, such as those connected to serial digital data transmission links.
2. Description of Related Art
An integrated circuit package ordinarily comprises a system of conductors supported by an insulating material and intended to connect the input-output terminals of an integrated circuit to the respective terminals of a connecting substrate, such as a printed circuit board. The terminals of the integrated circuit are divided into signal terminals and terminals for supplying the integrated circuit with electrical power. The continual increase in the frequency of the signals processed in an integrated circuit and in the transmission rate of the data entering and leaving the integrated circuit poses an increasingly acute problem for the fabrication of an integrated circuit package. Within the package, the connecting conductors and their insulating substrate have inductive and capacitive components which are no longer negligible. These parasitic components constitute a substantial obstacle to increasing the frequency of the signals and the transmission rates.
It is known, particularly from the EP Patent 0 368 740 and U.S. Pat. No. 5,254,871 that the parasitical effects of the inductive components can be reduced by incorporating potential planes into the package. These planes are disposed so as to be connected to the respective planes of the printed circuit board and to the nearest supply terminal of the integrated circuit. According to an improvement also disclosed in that patent, the supply conductors serve as an electromagnetic screen for the signal conductors. Each supply conductor is positioned between two groups of signal conductors in order to reduce interference between the signals of the two groups.
However, these means have as yet proven insufficient to satisfy the conditions currently desired. Transmission rates can reach several gigabaud. It is known that the theoretical speed of a signal in a conductor is equal to the light velocity divided by the dielectric constant of the material. A rate of one gigabaud translates into the presence of a small electron packet, representing one data bit, approximately every 20 cm along the conductor. This distance is reduced to about 5 cm for a rate of 4 gigabaud. Therefore, it is important that these electron packets not be disturbed by the passage of other packets flowing through adjacent conductors. This interference can translate into a reduction of the electron packet or a dispersion of the packet, as well as into small parasitical electron packets interposed between the packets of the signal. Under these conditions, the noise corresponding to the parasitic electrons becomes substantial relative to the desired signal. The extent of the noise is further increased due to the fact that the leading edges of the desired signal can be attenuated as a result of a reduction or a dispersion of the corresponding electron packets. Thus, it becomes very difficult to restore the signal received. Moreover, if the signal is subject to one or more reflections due to interfaces produced by insufficient impedance matching, electrons will separate from each packet and constitute parasitic groups, rendering correct transmission of the signal impossible.
Another problem is posed by the coexisting transmission of signals of different natures in the same package. This is particularly the case when a package intended for an integrated circuit is used for both data signal processing and for data transmission. In a multinodal information system, for example, an internodal communication module in each node is used to process data in cooperation with a processor, for example in order to implement a procedure for searching for data located in another node, and is used for internodal serial data transmission at very high speed, greater than one gigahertz. The incorporation of this module into an integrated circuit poses a problem. For example, in a node incorporating one or more processors of the type known by the trade name PowerPC 620 registered by the IBM company, the processing of the data is done in a first section of the integrated circuit adapted for CMOS type switching. According to this type, the buffer amplifiers used as input-output interfaces for the signal terminals of the integrated circuit are adapted for leading edges of 3.3 volts and can tolerate noise on the order of one volt. An important source of noise is the variation of the supply potentials over time due to the inductive and capacitive components of the supply conductors. The importance of these components is reduced as a result of the voltage planes in the package. However, the fluctuation of the potentials remains high due to the relatively high leading edges of the section (3.3. volts) and the high instantaneous intensities of the current required for the proper functioning of the integrated circuit (up to five amperes). Another cause of fluctuation is the small size required for the supply conductors in the integrated circuit, which therefore have a non-negligible resistance added to the inductive and capacitive components of the external conductors. The integrated circuit also contains a second section used for the serial digital transmission of data at very high speed. In this case, the amplitude of the transmission signals is less than one volt, on the order of 0.6 to 0.8 volts, that is on the order of the noise tolerated in the first section.